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Full text of "Handbook Of Chemical Engineering - I"

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CRUSHING AND GRINDING
199
APPROXIMATE POWER REQUIRED FOR               Secondary Crushing.After the
BLAKE JAW BREAKERS                   work of the primary breakers has
been done, the rock is in pieces varying according to the size of the original breaker, from 2 or 2 K up to 6 in. in diameter. In industrial use, the rock, unless it be limestone flux or ore for furnace use, requires further reduction; therefore a second stage in reduction is requiredthis stage we classify as crushing. It may be performed in machines of a number of different kinds.
Ordinarily, crushing is done in machines of the same type as those used for primary breaking, but of smaller size and delivering a smaller product. Jaw crushers may be and are used quite often, but are not particularly well adapted for this kind of work because of the variable character of their products. Gyratory breakers of small size are often used and these are much more satisfactory, since they deliver a product more uniform in size, more cubical in character and have much greater capacity than crushers of the Blake type. Small gyratory crushers, operating at high speed, are available for this purpose and are very largely used. The characteristics of the jaw and gyratory types have already been described.
SIZE	HORSEPOWER    SIZE		HORSEPOWER
10 by   7	7	48 by 36	150
12 by   9	10	48 by 42	150
16 by 10	12	54 by 42	150
24 by 10	14	60 by 42	160
28 by 13	25	60 by 48	175
30 by 15	30	60 by 60	200
36 by 18	40	84 by 60	225
42 by 24	50	90 by 60	250
48 by 26	60	96 by 60	275
48 by 30	110		
FIG. 4.Swing-hammer crusher.
In addition to the gyratory and jaw types for crushing, there are others that are very largely used, among these may be mentioned the swing-hammer type, the roll type and other specially designed machines.
The Swing-hammer type of machine ordinarily consists of a central shaft to which are connected a number of hammers so pivoted as to swing freely. In operation, this central shaft revolves at high speed, the hammers swinging straight out through the effect of centrifugal force. The rock to be broken is fed over a breaking plate so set that the swinging hammers just miss touching it in their revolution. The hammers strike the rock and the impact of this blow while the rock is resting upon the breaker plate, breaks it into pieces. Since